Of all the tax breaks on the fiscal cliff chopping block, the 95-year-old deduction for charitable giving would seem to stand a particularly good chance against budget-cutters.

That’s because it works.

Unlike with many of the tax loopholes being targeted for changes, years of research and polling have found that allowing Americans to deduct a percent of their charitable gifts from their tax bill not only cuts their tax liability — it also makes them more generous than they might otherwise be.

And it’s hard to find an elected official in either party who will oppose money going to charitable causes.

“I generally take the position that everything should be on the table,” the Senate Finance Committee’s top Republican, Orrin Hatch, told POLITICO. “However, I have a concern about the charitable deductions because a nation that doesn’t encourage charitable giving is a nation that has lost its way.”

But that doesn’t guarantee it will survive.

In this age of austerity — and just in time for the holidays, traditionally a busy time for giving — the effectiveness of the tax benefit is under scrutiny. Suggestions are coming from all directions. Republicans are pondering deduction caps, President Barack Obama is again proposing to limit the deduction, and budget groups and think tanks recommend turning it into a tax credit. Charities, foundations and nonprofits are lobbying hard to protect the tax break in fiscal cliff negotiations, and will do so again in an expected Tax Code rewrite next year.

Termed a tax loophole by some, the deduction will take $246.1 billion out of the federal Treasury over the next five years, according to figures from the Joint Committee on Taxation.

It’s a huge advantage for wealthy taxpayers, who pay higher marginal rates and therefore can deduct more per dollar in tax savings on average than lower income taxpayers — and reduce their tax bills by giving away vast sums of money to charity.

But that also makes the politics of the charitable deduction complicated. While Democrats are insisting that taxes go up on the wealthy, charities need wealthy donors to fund their operations.

A change “would have an incredible impact on universities and nonprofits, and that impact needs to be understood,” Sen. Ben Cardin (D-Md.), also a Finance panel member, told POLITICO. “This is something that needs to be done with a great deal of care.”

Some charitable groups say they have been awkwardly drawn into the middle of the battle between Obama and House Republicans over whether taxes on the wealthy should rise through increased tax rates or scaled-back deductions.

Regardless, supporters are already up in arms; two dozen groups swarmed Capitol Hill last week to tout the deduction’s importance. United Way polling estimates that 30 percent of taxpayers that use the deduction would scale back on giving if the benefit was reduced or eliminated.

“It’s something that has been built into the fabric of how Americans are accustomed to now thinking about how they support organizations and communities and issues they care about it,” said Stacey Stewart, U.S. president of United Way Worldwide.

The deduction has stayed in the Tax Code, mostly unchanged, since the War Revenue Act of 1917 because of the broad support it has from the country’s charities and foundations, which now number around 1.2 million. The tax benefit applies to donated money, land, building and cars — there’s even pending legislation to make wild-game meat eligible as a charitable deduction.

An Indiana University study found for every one cent in additional tax benefit, donors increase contributions by slightly more than 1 percent. For every dollar deducted, communities see $3 in benefits, according to an estimate from Leadership 18, the organization spearheading a current lobbying effort to protect the tax break in fiscal cliff negotiations.

The charitable tax break also directs money into poor and needy communities, noted United Way’s Stewart.

But critics question the need for a federal subsidy for altruism. Some tout — and some lament — the fact that the tax benefit also amounts to a large subsidy to religious organizations. And the deduction allows some taxpayers to avoid capital gains on money and property they donate.

Moreover, for all the support, there are still questions about how much the deduction actually incentivizes additional giving.

Joseph Cordes, an economics professor at The George Washington University, wrote in 2011 that recent studies have evaluated the deduction’s “price elasticity,” and found that “the deduction does not stimulate more charitable giving.”

And the deduction’s “upside-down” nature — the fact that the wealthy receive more tax savings than lower-income taxpayers because of their higher tax rates — makes it a target.

According to JCT figures, the top 3 percent of taxpayers gave about 45 percent of the $180 billion in deductible contributions last year. A Tax Policy Center study using that data estimates that the top 3 percent of earners get nearly 55 percent of the deduction’s total tax benefit.

Joseph Minarik, a former top economist in Bill Clinton’s Office of Management and Budget who is now director of research for the Committee for Economic Development, questions whether the “charities [the wealthy] espouse should benefit more from the public treasury than the charities supported by those with more modest incomes.”

Before the last scrubbing of the Tax Code in 1986, any taxpayer could claim a charitable contribution on their returns. But after a torrent of proposed curbs — including both a 14 percent cap and a $100 floor — the White House and Congress limited the deduction to only those who itemize their returns.

The Simpson-Bowles deficit commission in 2010 advocated turning the deduction into a 12 percent nonrefundable tax credit, available only after taxpayers donated at least 2 percent of their income.

And earlier this month, the Center for American Progress — a liberal think tank with close ties to the Obama administration — proposed changing the deduction into a uniform 28 percent credit.

Obama himself has repeatedly proposed that instead of allowing earners in the top two brackets to claim the deduction at the same level as their marginal tax rate, Congress should impose a 28 percent cap.

Republicans, who are eager to rewrite the Tax Code next year, have been careful in their approach. House Speaker John Boehner’s fiscal cliff offer last week proposed raising $800 billion in new tax revenue through loophole closing, but did not mention any deduction by name.

Still, many Republicans have latched on to the possibility of a broad cap on the value of the deductions taxpayers can claim — a move first proposed by Romney, and one that could hurt charities, since many taxpayers would fill up their “bucket” of deductions with things like the mortgage interest and state and local tax deductions.

Both sides have tried to position themselves as the tax break’s defender.

When the White House asked charities and nonprofits for their help in pushing for higher tax rates last week, Hatch and House Ways and Means Committee Chairman Dave Camp accused the White House of using scare tactics and “intimidation.”

Obama argued last week on Bloomberg TV that repealing the deduction would mean “every hospital and university and not-for-profit agency across the country would suddenly find themselves on the verge of collapse.”

According to an estimate from the White House’s National Economic Council, a $50,000 deduction cap would decrease giving by $150 billion over 10 years. And a $25,000 deduction cap would cause a $200 billion reduction in giving over the same period.

Minarik said the fairest way for the government to support giving would be through a credit, since a cap or a limit on deductions would create a system in which the wealthy “bundle” giving into one year to gain the best tax benefit, leaving charities with an unstable stream of donations.

“Caps cause problems,” Minarik said, because “high-income individuals could decide there is no reason to give.”